Not applicable
1. Field of the Invention
The present invention relates to Suzuki-Miyaura cross-coupling reactions. More particularly, the present invention relates to catalysts for Suzuki-Miyaura cross-coupling reactions.
2. General Background of the Invention
The Suzuki-Miyaura cross-coupling reaction, involving the coupling of an arylboronic acid with an organohalide, has proven to be an extremely useful synthetic tool in organic synthesis (1). Although palladium complexes bearing tertiary phosphine ligands are commonly employed (1a) (2), in Suzuki-Miyaura cross-couplings, these catalysts are often sensitive to air oxidation and therefore require air-free handling in order to minimize ligand oxidation. Nucleophilic N-heterocyclic carbenes, the imidazol-2-ylidenes, have recently been used as ancillary ligands for Suzuki-Miyaura cross-coupling reactions with great success (3).
In the specific area of coupling chemistry, catalytic systems which contain supporting ligations other than tertiary phosphine represent a scarcely explored area of investigation. Recently, a Pd(II) cyclometallated imine catalyst able to mediate both Suzuki (4) and Heck (5) reactions has been reported by Milstein. Unfortunately, this system requires high reaction temperatures and leads to products in modest yields.
Incorporated by reference are the paper attached to our U.S. Provisional Patent Application Serial No. 60/274,125 and entitled: xe2x80x9cConvenient and Efficient Suzuki-Miyaura Cross-Coupling Catalyzed by a Palladium/Diazabutadiene Systemxe2x80x9d by Gabriela A. Grasa, Anna C. Hillier, and Steven P. Nolan, all references cited therein, and all related papers of which the inventors are authors.
The following U.S. Patent is incorporated herein by reference:
U.S. Pat. No. 6,316,3 80 entitled xe2x80x9cCatalyst system comprising transition metal and imidazoline-2-ylidene or imidazolidine-2-ylidenexe2x80x9d
The present invention includes a Pd(OAc)2/diazabutadiene system for the catalytic cross-coupling of aryl halides with arylboronic acids and a method of catalytic cross-coupling of aryl halides with arylboronic acids using this system.
Based on the Milstein report, we thought a well-known family of ligands, the diazabutadienes, might possibly mediate the Suzuki-Miyaura reaction. The chelating nature of these ligands might also assist in stabilizing catalytic species. Ligands containing the 1,4-diaza-1,3-butadiene skeleton, a-diimines, (DAB-R, Scheme 1xe2x80x94see below) have been known for quite some time (6). The coordination versatility of these ligands, a consequence of the flexibility of the NCCN backbone and the strong s-donor and p-acceptor properties, reflects a very important feature of DAB-R-metal complexes (7). Few investigations have focused on the influence of DAB-R as a supporting ligand in catalytic processes. The most notable exceptions have been the use of metal-diimine complexes to mediate olefin polymerization (8) and alkyne cyclotrimerization (9) processes.